FIG. 1 is a schematic side view of a known air bag system 50 as installed in a compartment of the hub of a steering wheel 51, and FIG. 2 is a developmental view of parts of the interior of the air bag 52. In the event of a collision, an inflator (not shown) releases a gas rapidly into the air bag 52, thereby inflating it. It is known that there are advantages to having the bag assume a somewhat flattened, thick disc-like shape at the completion of filling and to provide inflation-controlling members 53 within the air bag to establish the desired shape. The members, which are usually fabric bands connected between the center of the gas filling side and the center of the impact side of the bag 52, hold the center of the impact side at a fixed distance from the inflator so that the gas is deflected laterally to fill the bag perimeter 52A. The thick disc-like shape best protects the occupant as he or she is thrown forward.
In a known arrangement, four equally spaced-apart inflation-controlling straps 53 (only one is shown in FIG. 2) are joined to a fastening member 55A by stitching 56A, and the fastening member 55A is stitched to the air bag 52 around the gas inlet opening 54. The fastening member 55A, in addition to providing for attachment of the straps 53, reinforces the air bag 52 in the region where it is attached to the inflator. Holes 57 are punched in the bag 52 and the fastening member 55A for fasteners that attach the air bag to the inflator. Similarly, an annular fastening member 55B provides for attachment of the straps 53 to the impact side of the bag 52 and reinforces the bag in the attachment region. The straps 53, fastening member 55B and the bag 52 are stitched together by three concentric circular stitch lines 56B.
When the air bag 52 is inflated, the gas jet is directed against the center part of the impact side, which is propelled rapidly toward the occupant until its movement is arrested by the inflation-controlling members 53. Stopping the movement of the center part of the impact side of the bag imposes high impact tensile forces on the members 53. Those forces produce high degrees of stress concentration in the portions of the straps where they join the fastening members 55A and 55B, namely, the areas indicated by the arrows "a" and "b" in FIG. 2. Accordingly, there is some chance that the inflation-controlling members 53 will separate from one or the other of the fastening members 55A and 55B along the stitching 56A or 56B, thereby allowing the bag to fill in an undesired way and possibly attain a less than optimum shape.